PART VIII.—THE OXALIC ACID GROUP OF POISONS. 
§ 714. Oxalic acid is widely distributed both in the free state and 
in combination with bases throughout the vegetable kingdom; and it 
also occurs in the animal kingdom. In combination with potash it is 
found in the Geranium acetosum (L.), Spinacia oleracea (L.), Phytolacca 
decandra (L.), Rheum palmatum (L.), Rumex acetosa, Atropa belladonna, 
and several others ; in combination with soda in different species of 
Salsola and Salicornm ; and in combination with lime in most plants, 
especially in the roots and bark. Many lichens contain half their 
weight of calcic oxalate, and oxalic acid, either free or combined, is 
(according to the observations of Hamlet and Plowright 1 ) present in all 
mature non-microscopic fungi. Crystals of oxalate of lime may be 
frequently seen by the aid of the microscope in the cells of plants. 
According to Schmidt, 2 this crystallisation only takes place in the fully 
mature cell, for in actively growing cells the oxalate of lime is entirely 
dissolved by the albumen of the plant. 
In the animal kingdom oxalic acid is always present in the intestinal 
contents of the caterpillar. In combination with lime, it is constantly 
found in the allantois liquor of the cow, the urine of man, swine, horses, 
and cats. With regard to human urine, the presence or absence of 
oxalate of lime greatly depends upon the diet, and also upon the indi¬ 
vidual, some persons almost invariably secreting oxalates, whatever 
their food may be. 
§ 715.^ Oxalic Acid, H 2 C 2 O 4 2H 2 O(90 + 36), specific gravity 1-64, 
occurs in commerce in prismatic crystals, very similar to, and liable to 
be mistaken for, either magnesic or zincic sulphates. The crystals are 
intensely acid, easily soluble in water (1 part requiring, at 14-5°, 1046 
parts of water) ; they are also soluble in 2J parts of cold, and readily in 
boiling, alcohol. Oxalic acid is slightly soluble in cold absolute ether ; 
but ether, although extracting most organic acids from an aqueous 
solution, will not extract oxalic acid. 
Oxalic acid sublimes slowly at 100°, but rapidly and completely at 
150° ; the best means of obtaining the pure anhydride is to put a 
1 Chem. News, xxxvi. 93. 2 Ann. Chem. Plicirm., lxi. 297. 
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